1. Field of Invention
The invention relates to a microchip for executing blood analysis by an absorption spectrometric process. The invention relates especially to a microchip which is used to measure the amount of an enzyme, such as GTP (glutamyl-trans-peptidase), γ-GTP or the like, and which is needed, for example, to diagnose liver function of the human body.
2. Description of Related Art
Recently μ-TAS (μ-Total Analysis System) has been considered, in which chemical analyses and the like are performed in a more precise manner using micromechanical engineering instead of a conventional device. In the case of using μ-TAS for medical fields there are the following advantages:
(1) By reducing the amount of sample, such as, for example blood, the burden on the patient can be reduced.
(2) By reducing the amount of reagent, the examination costs can be reduced.
(3) Since the device is small, the examination can be easily carried out.
It is considered that using these advantages the patient himself can carry out blood analysis at home, a blood analysis device using a microchip being used as a family specification.
In analysis by an absorption spectrometric process using a microchip, the concentration of a desired enzyme which is contained in the plasma can be measured by carrying out the series of operations described below. These operations are:
(1) Blood which was taken using a painless needle is delivered into the chip.
(2) The blood in the chip undergoes centrifugal treatment and is separated into plasma and hematocytes.
(3) The plasma and reagent are uniformly mixed with one another using a mixer and a mixture is produced therefrom.
(4) The mixture is delivered by means of a suction pump into a sensing chamber.
(5) The mixture which was delivered into the sensing chamber is irradiated with light from a light source and the attenuation of the light at a certain wavelength is measured.
A method of analyzing the concentration of an enzyme which is contained in the blood, such as, for example GTP, γ-GTP or the like, and which is needed to diagnose liver function, is disclosed, for example, in Japanese patent disclosure document JP 2004-109099 A. This publication describes a process in which light which is emitted from a light source, such as a light emitting diode or the like, which is incident from the top of the chip, which is totally reflected in an extremely small channel in the chip which is filled with an analysis sample, such as, for example, plasma, and which then emerges on the top of the chip, and is received by a detector, such as a silicon photodiode or the like.
However, the light emitted by the light emitting diode is scattered light. It is extremely difficult to cause the light incident in the chip to be totally reflected overall in an extremely small channel. Therefore, there is the disadvantage that the absorbance cannot be measured with high precision. The measurement of absorbance by the arrangement both of the light source as well as of the detector on the top of the microchip as described in the aforementioned publication causes the occurrence of measurement errors; this is not desirable.
On the other hand, Japanese patent disclosure document JP-2004-77305 A describes a process in which light from a light source can be incident from one side of a microchip, in which the light is absorbed by a sample with which an extremely small channel in the microchip is filled, and in which the transmitted light which emerges from the other side is measured. It can be imagined that, in this process, absorbance can be measured with high precision when blood is used as the sample.
In a microchip, due to its small size, there is a separate task. To measure the absorbance, a suitable extinction length is necessary. In order to keep the amount of the sample and of reagent small, there is no other method than making the area of the light incidence surface and the light exit surface in the sensing chamber extremely small.
If, in this way, the sensing chamber has a very narrow shape, the effect of the state of the light incidence surface and the light exit surface on the transmission factor in the sensing chamber is large. Since a microchip normally is made of a macromolecular material, damage easily occurs in the case of contact with a surrounding device when setting on a device for measuring the absorbance. Furthermore, there is a case in which contaminants, such as sebum, adhere to the light incidence surface and the like when the user handles it with bare hands. In this case, the absorbance cannot be exactly measured due to the adverse effect of a rough surface of the light incidence surface, resulting in the disadvantage that the concentration of the enzyme which is contained in the measurement sample cannot be exactly determined.